Stability of the COVID-19 At-Home Test after Exposure to Extreme Temperatures

ABSTRACT To ensure sufficient sensitivity and specificity of lateral flow tests for the detection of SARS-CoV-2 antigen, manufacturers recommend appropriate conditions for storage, including a temperature range. However, there is a high likelihood that kits will be exposed to temperatures outside of this range during transit to some regions. In this prospective study, we evaluated the sensitivity and specificity of the COVID-19 At-Home Test kits (manufactured by SD Biosensor/distributed by Roche) currently being delivered through a US Government program, after exposure to a range of hot and cold temperatures. COVID-19 At-Home Test kits were stored at up to 5 different temperatures: frozen (−4.0°F [−20.0°C]), refrigerated (42.8°F [6.0°C]), room temperature (68.0°F [20.0°C]), warm (98.0°F [36.7°C]), and excessive heat (118.0 to 126.0°F [47.8 to 52.2°C]) for 24 h and left at room temperature for 60, 90, or 120 min before use. Test kits were also stored for 48 h, 1 week, or 2 weeks in frozen, warm, and excessive heat conditions, and left for 60 or 120 min before use. In each scenario (storage temperature + time at room temperature), 5 positive and 5 negative control samples were applied, and line intensity was recorded using a color scale (0 to 100%). In every scenario, every positive sample resulted in strong signal intensity (≥26%), and every negative sample returned a negative result. This study suggests that exposure of up to 2 weeks to extreme temperatures, such as those that may occur in transit, does not impact the stability of the COVID-19 At-Home Test. IMPORTANCE COVID-19 At-Home Test kits may be exposed to extreme temperatures in transit, which may impact test sensitivity and specificity. We investigated assay ability to identify SARS-CoV-2 antigen after 24 h to 2 weeks in frozen, refrigerated, room temperature, warm, or excessive heat conditions. The assay correctly identified all positive and negative samples in all scenarios. This study suggests that exposure of up to 2 weeks to extreme temperatures, such as those that may occur in transit, does not impact the stability of the COVID-19 At-Home Test.

data suggest that exposure to extreme temperatures for up to 2 weeks is unlikely to impair the sensitivity or specificity of this assay. However, the authors have only evaluated the performance of only one Lateral Flow Assay (the COVID-19 At-Home Test kits (manufactured by SD Biosensor/distributed by Roche)) currently being delivered through a US Government program).
This represents a major weakness. The lack of evaluation of other rapid diagnostic tests makes it impossible to extend the study findings to other commercial tests. This point should be clearly emphasized by the authors to avoid a false sense of security on the part of health care users and the public.
The viral load of the positive control sample should also be clarified.
With attention to the above details, the paper is worth to be published.

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Reviewer #1
This is a well written paper demonstrating that one SARS-CoV-2 rapid antigen test is very robust when it comes to exposure to extreme temperatures. The only thing that could be improved are the tables. A summary of the distribution of values for the positive results for the 5 positive samples would be very helpful.
Response: Thank you for this positive review. While we agree that it would be helpful to provide a distribution of values, unfortunately we were unable to quantify the positive samples based on the starting material and so were unable to quantify the viral load relative to the color intensity (please see response B to reviewer #2). Given this challenge, color intensity was recorded as per the table below at the time of testing. All positive tests were 3+ by these criteria (≥26% intensity; strong positive). Despite not knowing the specific concentration, these tests nevertheless unanimously demonstrated strong positive signals regardless of the extreme temperatures or durations that they were subjected to.

Reviewer #2
Authors aim to demonstrate that the COVID-19 At-Home Test has robust performance at extreme temperatures outside manufacturer recommendations. Overall, the paper is well written, and the authors have reached their objectives. The presented data suggest that exposure to extreme temperatures for up to 2 weeks is unlikely to impair the sensitivity or specificity of this assay. However, the authors have only evaluated the performance of only one Lateral Flow Assay (the COVID-19 At-Home Test kits (manufactured by SD Biosensor/distributed by Roche)) currently being delivered through a US Government 3 program).
A. This [the evaluation of only one assay] represents a major weakness. The lack of evaluation of other rapid diagnostic tests makes it impossible to extend the study findings to other commercial tests. This point should be clearly emphasized by the authors to avoid a false sense of security on the part of health care users and the public.
Response: Thank you, we have added the following statement to the discussion acknowledging this limitation: "Finally, this study only evaluated one rapid LFT point-of-care test kit, so we are unable to apply these results to other commercial tests." B. The viral load of the positive control sample should also be clarified.
Response: Thank you, this is a fair comment. Per the instructions for use (IFU) for the BD Veritor SARS-CoV-2 Control swab set, the positive "control swabs contain non-infectious, recombinant viral protein antigen with less than 0.1% sodium azide as a preservative." There is no information about viral load, and this information does not appear to be readily available. Unfortunately, when we tried to use contrived, quantified SARS material from SeraCare, the antigen components did not produce a result on the LFT. We also investigated the use of SARS-CoV-2 positive control swabs from Microbiologics; however we did not use the swabs in our status although we did not end up using their swabs in our study as the IFU states "Microbiologics guarantees each nucleic acid is present and can be amplified, and that surface proteins are detectable by an antigen assay but does not guarantee specific analyte concentrations." Ultimately, we are unable to provide a source of positive control swabs that could guarantee a titer or concentration range.
C. With attention to the above details, the paper is worth to be published.
Response: Thank you, we appreciate your positive review.